Network Address Translation( NAT)

Network Address Translation (NAT) allows you to convert one IP address in to another address. Address Translation process changes the IP address information in a packet to different address. NAT feature is introduced to solve two major issues faced in networking: face the shortage of IP addresses and hide the network scheme. Now the major function of Address Translation is to convert the private IP addresses in a network in to a public IP address. This tutorial explains the major functions, different types and working of NAT.

Different Types of Address Translation

Address Translation is of different types depends on the way and the number of IP addresses they translate.
  1. Static NAT

    In Static Network Address Translation, one IP address in a packet is translated to different IP address manually. It is one to one mapping.

  2. Dynamic NAT

    In Dynamic Network Address Translation, address translation device picks an IP address dynamically to convert from a list of allowed IP addresses. Dynamic NAT has two set of IP addresses. One is a list of IP addresses which are allowed to be converted and the second is the list of IP addresses which are to be converted. The major problem with static and dynamic NAT is, they convert just one IP address  to another IP address. NAT cannot convert multiple IP addresses to single public IP address or vice versa.

  3. Port Address Translation

    Port Address Translation (PAT) helps all the private IP addresses in the network to use single public IP address with different port numbers. So by using PAT we overcome the limitation of NAT which uses one to one mapping. One disadvantage of PAT is, not all applications work with it. PAT works with only TCP and UDP protocols.

  4. Port Address Redirection

    Port Address Redirection (PAR) is the reverse of PAT. In PAR, multiple public IP addresses will be converted to single private IP address. PAR too works with only TCP and UDP protocols.

Major Benefits of Network Address Translation
  1. Address Translation fixed the scarcity of IP addresses

  2. NAT successfully hides internal network design from external parties

  3. NAT helps network admins to have tighter control over network traffic

Disadvantages of Address Translation

Though NAT is very helpful, it is not free from disadvantages. Some of them are:
  1. PAT and PAR works with only TCP and UDP protocols

  2. Not all applications support Address Translation

  3. Address Translation cause extra delay in each connection

  4. NAT makes network troubleshooting more complex

Recommended Tutorials
  1. Dynamic Host Configuration Protocol (DHCP)

  2. OSI Reference Model

  3. Virtual Router Redundancy Protocol (VRRP)

  4. What is a Router & Major Routing Protocols

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Dynamic Host Configuration Protocol (DHCP) CCNA Exam Tutorial

The Dynamic Host Configuration Protocol (DHCP) allows devices to dynamically get IP address information. It is very important in networks especially for big networks because it assigns IP addresses to each devices in the network automatically. Think about a network having thousands of devices. It is very difficult to assign static IP addresses to each devices without having errors. Here Dynamic Host Configuration Protocol helps us. This protocol assigns IP address to each device without any errors and is very easy to manage. It contains two parts, server and client.


Working of Dynamic Host Configuration Protocol

We can simply use the term DORA to explain the working of DHCP. It is a four stage process and each stage is explained below.

  1. D-- DHCP Discovery

    When a client connected to a network, it sends broadcast to discover the DHCP server. This broadcast is termed as DHCPDISCOVER.

  2. O--- DHCP Offer

    At this stage, server responds to the client DISCOVERY message and sends a DHCPOFFER unicast message. DHCPOFFER includes IP address, subnet mask, default gateway address, DNS address etc.

  3. R---- DHCP Request

    Here client sends a DHCPREQUEST message to the server.

  4. A--- DHCP Acknowledgment

    Here server sends an acknowledgment (DHCPACK) to the client indicating it received the DHCPREQUEST from the client and client accepted the IP address information.

Advantages of Using DHCP

Major advantages of using Dynamic Host Configuration Protocol are:
  1. Very less chances to get IP addressing errors

  2. Efficient control on IP addressing in a network because it is centralized.

  3. We can avoid the heavy work of manual IP addressing

Suggested Topics
  1. How to Configure a Computer to Receive Automatic IP Address

  2. Interior Gateway Routing Protocol (IGRP)

  3. Internet Group Management Protocol (IGMP) Tutorial

  4. Working Of Remote Procedure Call (RPC)in Session Layer

Cisco Certification Exam Tips

If you are preparing for Cisco certification exams like CCNA, you must have good knowledge in DHCP. If you follow CCNA dump for your next exam, the dotted information might help you. Some important points to remember about Dynamic Host Configuration Protocol for your Cisco Certification exams are listed below.
  • Command to Enable or Disable DHCP on Cisco IOS Router --service dhcp

  • Cisco Command to create address pool -- ip dhcp pool

  • Command to assign domain name to client --domain-name

  • Command to specify DHCP IP range -- network

  • Command to check if server can use an IP address in the pool -ip dhcp ping timeout

  • Command to exclude an IP address from the DHCP address pool --ip dhcp excluded-address

  • Show addresses assigned to clients --show ip dhcp binding

  • DHCPNACK - This acknowledgement from server tells the client the offer is no longer valid

  • DHCPDECLINE - Client tells the server, it cannot use the offer from the server

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